Magnetic recording media are widely used in various applications, e.g., in hard disk form, particularly in the computer industry, for storage and retrieval of large amounts of data/information. These recording media are conventionally fabricated in thin film form and are generally classified as “longitudinal” or “perpendicular”, depending upon the orientation (i.e., parallel or perpendicular) of the magnetic domains of the grains of the magnetic material constituting the active magnetic recording layer, relative to the surface of the layer.
In the operation of magnetic media, the magnetic layer is locally magnetized by a write transducer or write head to record and store data/information. The write transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field applied by the write transducer is greater than the coercivity of the recording medium layer, then the grains of the polycrystalline magnetic layer at that location are magnetized. The grains retain their magnetization after the magnetic field applied by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The pattern of magnetization of the recording medium can subsequently produce an electrical response in a read transducer, allowing the stored medium to be read.
In conventional hard disk drives, data is stored in terms of bits along the data tracks. In operation, the disk is rotated at a relatively high speed, and the magnetic head assembly is mounted on the end of a support or actuator arm, which radially positions the head on the disk surface. By moving the actuator arm, the magnetic head assembly is moved radially on the disk surface between tracks.
Lithographically patterned media, also known as bit-patterned media, are being pursued to increase areal recording density as compared to conventional recording media. Bit-patterning combines several hundred media grains into one single magnetic island, which does not require large coercivities. The manufacturing of lithographically patterned media typically involves using photolithography techniques to form a pattern of discrete and separated magnetic regions. This may include a nanoimprint process, i.e., the stamping of soft resist materials with hard stampers to mold a pattern within the resist.
As the size and spacing of magnetic device features have decreased to increase recording density, the height of the steps of these features have increased. Also, as the number of layers deposited during the manufacture of magnetic devices increases, irregularities in the surface of the layers increases. As a result, chemical mechanical polishing (CMP) may be used to planarize feature surfaces during processing.
CMP is used to remove surface topography in order to achieve planar surfaces suitable for photolithographic patterning of complex patterns. Material is removed during a CMP process by a combination of chemical etching and mechanical abrasion. CMP processes typically have a material removal rate of 300 to 500 nanometers (nm) per minute under normal process conditions. Removal continues until an endpoint is reached, which is theoretically the point where all of the excess material is removed, and a smooth planar surface remains.
The CMP endpoint may be determined by a variety of techniques. For example, prior CMP processes have incorporated instruments to measure changes in the surface optical reflectivity, changes in the surface temperature, and changes in eddy currents induced through the layers. Other CMP processes alternatively use prior test runs to estimate polish time to the endpoint. However, these prior CMP endpoint detection techniques are subject to variations as to when the endpoints are detected. Thus, there is a need in the industry for a process capable of accurately detecting CMP endpoints for fabricating consistent and accurate features in bit-patterned media.